This invention relates to a terminal assembly for use in an industrial control system, particularly, a sequencer, and more particularly relates to a terminal assembly having improved positioning means for set screws with washers for connecting cables.
Terminal assemblies have been used, which include a main block made of an electrically insulating thermoplastic or thermosetting material such as a plastic material, contacts made of a conductive material such as a metal and press-fitted in the main block, cable insertion apertures for inserting the ends of conductive cables to be electrically connected to the contacts, and set screws with washers threadedly engaged in the main block for forcedly this bringing about the ends of the conductive cables into electrical contact with the contacts. After such a terminal assembly having the contacts press-fitted in its main block has been arranged at a predetermined position in a control system, the ends of predetermined conductive cables are inserted into the cable insertion apertures and then clamped and connected to the contacts by tightening the set screws with washers by means of a screwdriver or the like.
With such a hitherto used terminal assembly, however, before the assembly has been arranged at the predetermined position in the control system, the set screws with washers must be tightened to the full extent in order to avoid the set screws with washers from being dislodged from the terminal assembly. After arranged at the predetermined position, the set screws with washers are once loosened to provide sufficient spaces between the washers of the set screws and the contacts for inserting the ends of the conductive cables, and after the ends of the conductive cables have been inserted in the spaces, the set screws with washers are again tightened to finally connect the ends of the cables to the contacts.
Therefore, the operations loosening and secondarily tightening the set screws are needed which are tedious and time-consuming operations. Particularly, if insufficiently loosen the set screws in loosening operation, it will become difficult to insert cables into spaces between the washers and the contacts. On the other hand, if too loosen, there will be an increased risk of dislodgment of the set screws.
It is an object of the invention to provide an improved terminal assembly which eliminates the disadvantages of the prior art described above and which will be able to insure sufficient spaces between set screws and contacts for inserting ends of cables thereinto by means of improved positioning means for set screws, while preventing the set screws from being dislodged before the cables are connected to the terminal assembly without requiring any difficult operation.
In order to accomplish this object, in a terminal assembly including at least one contact having a connecting portion to be connected to a cable, a fixing portion to be fixed to a main block of said terminal assembly and a connection portion to be connected to a mating component; said main block made of an electrically insulating thermoplastic or thermosetting material for holding and fixing said contact and having at least one cable insertion aperture for said cable and at least one connection space for said contact and said cable; at least one set screw having a washer inserted in said main block for electrically connecting and fixing said cable to said contact; and at least one nut inserted in said main block for threadedly engaging said set screw having the washer; according to the invention at least one projection is provided at a predetermined position on the inside of a set screw receiving aperture formed in said main block for receiving said set screw to provide a sufficient space for inserting said cable between said contact and the surface of said washer facing to said contact when the forward end of said set screw contacts said projection.
The projection is preferably made of an elastic material such as rubber, other elastomers and elastic metals.
The projection may be formed integrally with the main block or may be formed separately from the main block and attached thereto with an adhesive.
The terminal assembly constructed as described above according to the invention can bring about the following significant effects over those of the prior art.
(1) According to the invention the main block of the terminal assembly comprises projections on the inner surfaces of the set screw receiving apertures so that the set screws can easily be positioned by bringing the ends of the set screws into contact with the projections when the terminal assembly is manufactured and shipped, while ensuring the sufficient spaces for inserting the ends of cables for their connection.
(2) With the terminal assembly according to the invention, as there are sufficient spaces between the contacts and the washers of the set screws for inserting the ends of cables to be connected when the terminal assembly has arrived at a customer, there is no need for loosening the set screws for connecting the cables by an operator of the customer, thereby enabling rapid connection operations to be performed with resulting reduction in cost and labor for manufacturing.
(3) The projections of the terminal assembly according to the invention have the elasticity to allow the repeated use of the terminal assembly connecting and disconnecting cables many times.
(4) The terminal assembly according to the invention is constructed to prevent the set screws with washers from being dislodged only by screwing them until contacting the projections, while only by screwing the set screws into the nuts by a screwdriver the projections are easily deformed to allow the set screws to advance, thereby enabling the ends of cables to be fixed to the contacts. As a result, the management of parts becomes easy.
The invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.